DESCRIPTION (Verbatim from the Applicant's Abstract): Recently, promising new MRI techniques using laser polarized aboutHe and arterial spin tagging (AST) have been developed for studying ventilation and perfusion (V/Q) in human lungs. In patients with emphysema and pulmonary emboli (PE), these techniques have produced dramatic images with the characteristic V/Q distributions of these diseases. While preliminary results indicate that this new integrated MRI technique can be used for studying regional V/Q abnormalities, the technique has not been clinically or physiologically validated. The ultimate clinical usefulness of this non-invasive imaging modality will only be possible if is validated by an established method. The main goal of this proposal is the refinement of V/Q imaging using polarized 3He and AST, and its validation in an animal model. This technique will then aid in the overall assessment of lung function and in the development of a model to quantify ventilation, perfusion, and physiologic V/Q relationships in the normal and diseased lung. We propose to validate 3He/AST method using single-photon emission computed tomography and the multiple inert gas elimination technique by accomplishing the following specific aims: 1. To establish the normal values of the regional helium distribution and perfusion signal in normal pigs. We will perform ventilation with hyperpolarized 3He and perfusion with AST. We will also perform the multiple inert gas elimination technique (MIGET) in each pig to confirm that its V/Q distributions are normal. 2. To obtain 3He ventilation and AST perfusion MRI in pigs after airway occlusion by various sizes of glass beads as an airway model for emphysema. 3. To obtain 3He ventilation and AST perfusion MRI in pigs with autologous clot inserted into their pulmonary artery as a model of PE. 4. 3He gas MRI and artenal spin-tagging perfusion scans will be used to deterrnine V/Q changes following the administration of streptokinase as treatment for the induced PE. Once validated, this integrated MRI method will provide novel anatormic and physiologic information for detection and treatment of pulmonary diseases.